In any rotating electrical device bearing noise is a significant contributor to the overall motor noise. In an electric motor with one or two sleeve bearings that are used for both axial thrust surfaces and cylindrical running surfaces, the bearing related noise consists of four main components:    1) Bearing/Shaft Friction Noise created by the interface of two sliding surfaces    2) Commutator Brush Noise/vibration transmitted through the commutator to the shaft to the bearing    3) Cogging Torque Noise transmitted from the cogging lamination in the magnetic circuit to the shaft to the bearing    4) Axial thrust surface noise caused by the interaction of the axial thrust washer and the bearing
All of these noises associated with the bearing are amplified when considering the noise/vibration path to the adjacent structure. Bearing/structure noise is created by vibration transferred to the adjacent resonating structure. Thus, there is a need to reduce these noises.